Impact of Array Mutual Coupling on Multiantenna Propagation-Based Key Establishment

While the impact of antenna mutual coupling on multiple-input multiple-output (MIMO) communication performance has been well documented, little work has appeared demonstrating how antenna coupling impacts the performance of multiantenna radios that use reciprocal electromagnetic propagation to establish secret encryption keys. This paper uses network theory to analyze the performance of such systems. The presentation includes an eavesdropper whose antennas may be very near and therefore coupled to the antennas of a legitimate node and further demonstrates the signal and noise model when the systems must remove the impact of nonreciprocal circuit elements through calibration. Representative results obtained with the model quantify the impact of coupling and the type of impedance matching used to connect the antennas to the radio circuitry on the system key establishment performance.